When clubbing is encountered in patients, doctors will seek to identify its cause. They usually accomplish this by obtaining a medical history—particular attention is paid to lung, heart, and gastrointestinal conditions—and conducting a clinical examination, which may disclose associated features relevant to a diagnosis. Additional studies such as a chest X-ray and a chest CT-scan may also be performed

Pathophysiology

The exact cause for sporadic clubbing is unknown, with numerous theories as to its cause. Vasodilation (distended blood vessels), secretion of growth factors (such as platelet-derived growth factor and hepatocyte growth factor) from the lungs, and other mechanisms have been proposed. The discovery of disorders in the prostaglandin metabolism in primary osteoarthropathy has led to suggestions that overproduction of PGE2 by other tissues may be the causative factor for clubbing

Important causes of clubbing in the adult:

Lungs

Lung Cancer (clubbing is in general an ominous sign for this, and remember “beware of the yellow clubbed digit”. (Yellow from nicotine, and clubbed from cancer).

Pus in the lung (bronchiectasis as in CF, but also lung abscess and empyema)

There are other causes of clubbing, outside the heart and lungs, but these are the important ones.

If a patient has painful wrists, painful ankles and comes to see you and you miss that they also have clubbing, you will go down the wrong path looking for RA etc, when what they have is Hypertrophic Pulmonary Osteoarthropathy. The causes of HPOA are the same as those of clubbing.

Pseudoclubbing: distinguished from clubbing by the preservation of the nail-fold angle and bony erosion of the terminal phalanges on radiography. Pseudoclubbing is also more likely to be asymmetric.